Fix fail on zero-size append

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Signed-off-by: Richard Weinberger <richard@nod.at>

fsstress.sh

diff --git a/fsstress.sh b/fsstress.sh
index 3b112b0..f74cb4c 100755
--- a/fsstress.sh
+++ b/fsstress.sh
@@ -88,8 +88,11 @@
 	do
 		SIZE=$(($RANDOM % $MAX_SIZE_MB))
 
-		dd if=/dev/urandom of=testdir/smallfile$i bs=1M count=$SIZE\
-			oflag=append conv=notrunc &> /dev/null
+		if [ $SIZE -gt 0 ]
+		then
+			dd if=/dev/urandom of=testdir/smallfile$i bs=1M count=$SIZE\
+				oflag=append conv=notrunc &> /dev/null
+		fi
 	done
 }
 
@@ -99,9 +102,12 @@
 	do
 		SIZE=$(($RANDOM % $MAX_SIZE_MB))
 
-		dd if=/dev/urandom of=testdir/smallfile$i bs=1M count=$SIZE\
-			oflag=append conv=notrunc &> /dev/null
-		sync
+		if [ $SIZE -gt 0 ]
+		then
+			dd if=/dev/urandom of=testdir/smallfile$i bs=1M count=$SIZE\
+				oflag=append conv=notrunc &> /dev/null
+			sync
+		fi
 	done
 }